https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94613
Bug ID: 94613
Summary: combine: Wrong code due to splitting a simplified
IF_THEN_ELSE
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: critical
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: krebbel at gcc dot gnu.org
Target Milestone: ---
Created attachment 48284
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48284&action=edit
autoreduced testcase
When compiling the attached testcase for IBM Z GCC optimizes an OR operation
away during combine leading to wrong code being generated:
cc1plus -O3 -march=z14 t.ii -quiet -o t.s
try_combine is invoked for the following 3 insns:
i1: 28: r111 = r110 | r158
i2: 31: r115 = r111 - r94
i3: 36: r122 = (r110 == 0 ? r115 : r177)
i3 becomes the following after inserting i1 and i2
36: r122 = (r110 == 0 ? r110 | r158 - r94 : r177)
simplification omits ORing r110 since it is 0 anyway:
36: r122 = (r110 == 0 ? r158 - r94 : r177)
after not being able to recognize the insn it gets split into parts again:
28: deleted
31: r115 = r158 - r94
36: r122 = (r110 == 0 ? r115 : r177)
